Fatigue Strength of Welded Tubular Aluminum Truss

Welded, tubular box trusses of aluminum alloy 6061-T6 were subjected to static and fatigue tests in bending. Experimental determinations were made of residual welding and bolting stresses as well as stresses resulting from the applied loading. Primary and secondary stresses in the members and local stresses at the joints due to the applied loads were calculated by the finite element method. The fatigue strength of the trusses was compared to that of small double strap fillet welded specimens. The fatigue strength of the tubular trusses was in reasonable agreement with the strength of the small joints when secondary bending stresses plus stresses due to local bending of the tube walls were considered in the analysis. Residual stresses due to welding and bolting did not appear to have much effect on fatigue life.